1. Field of the Invention
The invention relates to a multilayered hydrogen absorbing body formed by laminating a plurality of hydrogen absorbing materials capable of absorbing hydrogen.
2. Description of the Related Art
Recently, hydrogen energy has drawn widespread attention as clean alternative energy, amid growing concerns over environmental problems such as global warming due to emissions of carbon dioxide, and energy problems such as depletion of oil resources. In order to put hydrogen energy into practical use, it is necessary to promote development of technologies for storing and transporting hydrogen in safety. As hydrogen absorbing materials capable of storing hydrogen, carbon materials such as activated carbon, fullerene and nanotube, and a hydrogen absorbing alloy have been developed. Among these materials, the hydrogen absorbing alloy is promising as a novel transportable absorption medium, since the hydrogen absorbing alloy can store explosive hydrogen in a form of metal hydride, which is a safe solid substance, in high volume.
Many different types of hydrogen absorbing alloys are known. Among these alloys, much attention is focused on a magnesium alloy and a vanadium alloy since hydrogen absorption amounts thereof are large. However, the magnesium alloy is not appropriate for a practical use, since the magnesium alloy needs to be at a high temperature of at least 250° C. for absorption/desorption of hydrogen (hereinafter, referred to as “hydrogen absorption/desorption), and a speed at which the magnesium alloy absorbs/desorbs hydrogen (hereinafter, referred to as a “hydrogen absorption/desorption speed”) is low, although the hydrogen absorption capability thereof is high. In the case of the vanadium alloy, the hydrogen absorption amount is approximately 4% by mass. However, the vanadium alloy can desorb only approximately half of the absorbed hydrogen at temperatures near the normal temperature, and needs to be at a high temperature of at least 300° C. for desorbing the entire amount of the absorbed hydrogen. Accordingly, various attempts have been made in order to enhance hydrogen absoprtion/desorption characteristics of the magnesium alloy and the like having a large hydrogen absorption amount. For example, Japanese Patent Laid-Open Publication No. 2002-105576 discloses a hydrogen absorbing laminated structure including a hydrogen absorbing layer which is formed by thinning magnesium or a magnesium alloy, and a pair of hydrogen exchanging layers which sandwiches the hydrogen absorbing layer.
The hydrogen absorbing laminated structure disclosed in Japanese Patent Laid-Open Publication No. 2002-105576 is formed by providing the hydrogen exchanging layers on both sides of the hydrogen absorbing layer formed from magnesium or the like. The hydrogen exchanging layers function as catalyst layers in which hydrogen gas is dissociated in an atomic form. According to an embodiment, there is provided a three-layered hydrogen absorbing laminated structure which is formed by sandwiching the magnesium layer between a pair of palladium layers. In the three-layered hydrogen absorbing laminated structure, the hydrogen absorption speed is relatively high. However, the hydrogen desorption speed is not sufficiently high at temperatures near the normal temperature. Namely, even when hydrogen exchanging layers formed from palladium having a catalytic action are provided on both sides of the hydrogen absorbing layer formed from magnesium, hydrogen cannot be sufficiently obtained at temperatures near the normal temperature. Accordingly, the problem described above cannot be solved.